Last updated June 14th 2017

White bread is among the processed foods known to contain “bad carbs.” But is whole-wheat bread really better for you? A new Israeli study shatters this myth.

Conducted at the Weizmann Institute of Science, the study reveals that “wholesome” choices are not necessarily the healthiest for everyone. It all depends on the unique bacteria in our gut.

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Up to 40 percent of our diet

Bread accounts for about one-tenth of the calories many people in the West consume and up to 40 percent of the caloric consumption in some non-Western countries – more than any other food product. In the past few decades, since white bread has acquired a bad rep, bakeries have been going out of their way to produce high-quality whole grain breads.

But as it turns out, our individual microbiome – our specific intestinal microbes – will determine whether white bread is good or bad for us.

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In the study, recently published in the scientific journal Cell Metabolism, scientists compared two kinds of bread: One was industrial white bread made from refined wheat and considered less healthy; the other was sourdough-leavened bread made in an artisan bakery from freshly stone-milled whole grain wheat flour and baked in a stone hearth oven (it was prepared specially for the study and was assumed to possess superior properties).

The study’s 20 participants were divided into two groups and asked to consume large quantities of bread (supplying about a quarter of their caloric intake) for a week. One group ate the white bread, and the other, the sourdough bread. After a two-week break, they switched, and for a week the group that had previously eaten white bread ate the sourdough bread, and vice versa.

“No difference between the health effects of the two types of bread”

Tests revealed that eating bread of any kind affected the blood levels of sugar, minerals, liver enzymes and other substances. But when the scientists compared the effects of the two types of bread, they were surprised. “We were sure that the sourdough bread would come out a healthier choice, but much to our surprise, we found no difference between the health effects of the two types of bread,” Prof. Eran Segal, who led the study, said in a statement.

According to research team member Dr. Eran Elinav, that’s because “the body’s response to bread is a highly personal matter, so the differences among people in the study averaged themselves out.” His colleague Prof. Avraham Levy says: “We planned the experiment so that everyone would consume the same amount of available carbohydrates from both bread types. Because whole-wheat bread contains relatively fewer carbohydrates, this means that people ate more of it compared to the white bread. This difference in carbohydrate levels should also be taken into consideration when planning a diet.”

Which bread is better for you? It depends on your gut bacteria

The study further shows that about half of the participants had higher blood sugar levels after eating white bread, whereas the other half had higher blood sugar after eating sourdough bread. It is possible that these different responses were due to the differences in the individuals’ intestinal microbes – collectively known as the microbiome. The composition of the microbiome in the people whose response to white bread produced high blood sugar levels differed from that of the people who responded to sourdough bread with high blood sugar.

The scientists developed an algorithm connecting the microbiome’s composition with the person’s response to the type of bread. The algorithm was used to predict who will have high blood sugar after eating white bread, and who will have high blood sugar after eating the sourdough.

Additional researchers conducting this study include Tal Korem, Dr. David Zeevi, Dr. Omer Weissbrod, Noam Bar, Maya Lotan-Pompan, Dr. Tali Avnit-Sagi, Noa Kosower, Gal Malka, Michal Rein, Dr. Adina Weinberger, Dr. Niv Zmora, and Jotham Suez.

Photos and video: TiBineDaria Nepriakhina, Weizmann Institute

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